1. Field of the Invention
This invention relates to a composition for cleaning and etching the surface in fabricating electronic displays and the substrates.
Particularly this invention relates to a composition to effectively remove the contaminants by cleaning, to remove any contaminants on the surface, and to etch SiO.sub.2 and Si substrate in the fabrication process of electronic displays, quartz devices, wafer, and semiconductor wafer.
In case of Cathod Ray Tube(CRT) which is a very popular kind of electronic display, the fresh bulb should be cleaned by 10.about.18% Hydrofluoric Acid (HF) solution before coating process.
The cleaned panel is further processed to the next positions such as panel inner black coating, screen coating, lacquer spraying. aluminizing, funnel inner dag coating, panel/funnel frit sealing, neck washing, mounting and exhausting, funnel outer dag coating, panel face coating, etc.
For panel face coating, the coating materials may include In.sub.2 O.sub.3, Sb.sub.2 O.sub.3, SnO.sub.2, SiO.sub.2 and before face-coating the surface contaminants are removed by cleaning with HF solution 1.about.2% or ammonium bifluoride solution. The defective coating could be removed by using 10.about.30% ammonium bifluoride solution "before backing" and by using CeO.sub.2 "after backing".
In case of LCD, the manufacturing process of LCD may include cleaning, etching during lithography process, and it is important to etch uniformly and reproducially.
The types of materials to be cleaned and to be etched and the compositions for cleaning and etching solution for LCD and semiconductor wafer are shown in below table.
Cleaning(SiO.sub.2) 1. H.sub.2 SO.sub.4 :H.sub.2 O.sub.2 (6:1), 120.degree. C. 2. 50% HF:H.sub.2 O(1:100.about.1000) 3. NH.sub.4 OH:H.sub.2 O.sub.2 :H.sub.2 O(1:1:7) SC-1 4. HCl:H.sub.2 O.sub.2 :H.sub.2 O(1:1:6) SC-2 5. D.I. water rinse Etching(SiO.sub.2) 1. 40% NH.sub.4 F:50% HF(7:1) BOE 2. 40% NH.sub.4 F:50% HF(7:1) + H.sub.2 O.sub.2 Etching(SiNx) H.sub.3 PO.sub.4 :H.sub.2 O(85:1) or 40% NH.sub.4 F:50% HF(20:1) Etching(Al and Al alloy) H.sub.3 PO.sub.4 :CH.sub.3 COOH:HNO.sub.3 :H.sub.2 O (65:5:5:25)
The required conditions of above cleaning and etching solutions may include control of cleaning and etching rate, etching selectivity, control of etching profile, stability and homogeneity of the solutions.
In case of quartz devices which are used for manufacturing of wafer, the manufacturing process of quartz devices is as follows; raw material--cleaning (11.about.16.5% HF solution, 2.about.3 minutes)--waxing--Cutting and polishing--dewaxing--ultrasonic washing--cleaning (15% HF solution, 5 minutes)--benching--cleaning (11.about.16.5% HF solution, 5 minutes)--drying
High concentration of HF solution are used for removing the surface contaminants and thermally oxidized layer formed, but HF solution may cause problems relating to smoothness, etching damage, crack, etc. The quartz devices are contaminated during wafer fabricating process, specially in the process of heat treatment and deposition. HF solution is used for cleaning such contaminants of quartz devices.
In case of semiconductor wafer, the fabrication process may include:
I. Forming process of wafer
1. Growing of single crystal silicon PA0 2. Slicing PA0 3. Lapping (approx. 60 .mu.m by mechanical polishing PA0 4. Chemical polishing (approx. 30 .mu.m by etching) PA0 5. Polishing (approx. 10 .mu.m by 3 times polishing to acquire the desired roughness) PA0 6. Cleaning PA0 7. Initial cleaning PA0 8. Oxidization PA0 9. Ion dopping and diffusing PA0 10. Epithexial growth PA0 11. Forming of insulating and conductive layer PA0 12. Forming of polarity PA0 a) 0.1.about.50 wt % of fluoride(s), based on the total composition weight, and PA0 b) 0.8.about.40 wt % of at least one selected from the group consisting of sulfonic acid, sulfonate(s) and persulfate(s), based on the total composition weight, and PA0 c) optionally 0.01.about.10 wt % of inhibitor and/or 0.5.about.20 wt % of reaction accelerator, PA0 wherein sulfonic acid or sulfonate(s) is selected as component b), 0.2.about.40 wt % of alcohol and/or 0.2.about.40 wt % of persulfateare are added, and wherein persulfate(s) is selected as component b), 0.01.about.10 wt % of surfactant is added. PA0 a) nitrate(s), and PA0 b) fluoride(s), PA0 c) optionally at least one selected from the group consisting of reaction accelerators, and surfactants, PA0 wherein the weight ratio of nitrate(s) to fluoride(s) is in the range of 1:9.about.9:1 and the concentration of reaction accelerators is the range of 30.about.90%. PA0 a) fluoride(s), and PA0 b) oxalic acid and/or oxalate(s) PA0 c) optionally, at least one selected from the group consisting of sulfuric acid, phosphoric acid, and/or mixed acid of sulfuric acid and phosphoric acid, wherein the weight ratio of fluoride(s) to oxalate(s) is in the range of 1:9.about.9:1, and the concentration of sulfuric acid, phosphoric acid, and/or mixed acid of sulfuric and phosphoric acid is the range of 30.about.90%.
II. Fabrication process of semiconductor wafer
In the process of above 8.about.12, lithography steps are accompanied. As substrates pass through each process, chemical etching on silicon and silicon oxide is performed, and ionic and non-ionic contaminants and other contaminants formed on silicon and silicon oxide should be removed.
More details about the process to require cleaning and etching are described as below.
The oxidizing process (above No. 8) includes the pre-washing step before growing SiO.sub.2 layer on the substrate, however, the pre-washing solution such as solvent, sulfuric acid, and/or hydrogen peroxide may produce a thin-oxidized silica layer on the surface while washing. Such thin-oxidized silica layer should be removed by HF solution (HF:H.sub.2 O=10:1).
The diffusing process (above No. 9) includes washing step before diffusing. The washing solution such as mixed solution with sulfuric acid and hydrogen peroxide or mixed solution of ammonium hydroxide and hydrogen peroxide can usually remove organic contaminants and ionic contaminant by dipping for 10.about.20 minutes. However, such washing causes by forming of oxidized layer on the air-exposed part of silicon surface thus the oxidized layer should be removed by using diluted HEF solution.
In lithography process, etchant is used to define the ion injection/diffusing part and the shield part on the surface of substrate.
There are usually two kinds of etching, wherein one is wet etching (chemical etching) and the other is dry etching (plasma etching), however, lithography is deemed to be a kind of etching.
Wet etch is chemical etch to be performed by chemical reaction between chemical solution and the layer to be removed. The type of chemical and the composition ratio differ according to the kinds and characteristics of the layers.
The principles of wet etch is as follow.
There are two ways of creating SiO.sub.2 film, wherein one is thermal-grown SiO.sub.2 on silicon substrate, and the other is Deposit (CVD) SiO.sub.2 on various films. Any kind of etching method known in this art utilized the dissolving nature of HF.
Thermal-grown SiO.sub.2 film is etched by following reaction. EQU HF.fwdarw.H.sup.+ +F.sup.-
The isolated F ion reacts on SiO.sub.2 and etching is performed as follows. EQU SiO.sub.2 +4HF.fwdarw.SiF.sub.4 +2H.sub.2 O EQU 2HF+SiF.sub.4.fwdarw.H.sub.2 SiF.sub.6
From the above formula, F ion is reduced according as etching is proceeding and hydrogen concentration is decreased as the solution becomes diluted by produced H.sub.2 O. As a result, the etching rate changes and the process becomes unstable, which is disadvantageous to uniformity and reproductivity.
To standardize the etching rate, ammonium fluoride (NH.sub.4 F) can be added into solution. Ammonium fluoride dissociated ammonium ion from fluoride ion and the isolated fluoride ion participates in etching. EQU NH.sub.4 F.fwdarw.NH.sub.4 +F.sup.-
The reduction of F ion consumed for etching is compensated by adding ammonium fluoride and consequently the concentration of hydrogen can be maintained to keep the etching rate constant.
As almost wet enchants are isotropic (etching in all directions), the undercut is made. Excessive undercut usually occurs in the wet etch to cause resist lifting. This is the drawback of wet etch and consequently it is difficult to use wet etch in manufacturing high integrated circuit. Single crystal silicon and metal layer are etched after oxidizing, wherein nitric acid is used as oxidant. Single crystal silicon is oxidized to be SiO.sub.2 which should be etched by hydrofluoric acid.
The mixed acid to be made of HNO.sub.3 :HF:CH.sub.2 COOH or H.sub.3 PO.sub.4 =2.5:1:1 is used for etching single crystal silicon, wherein CH.sub.2 COOH or H.sub.3 PO.sub.4 serves to control the rapid and excessive reaction to be done by HNO.sub.3 and HF. However, as such control is still not sufficient, single crystal silicon wafer can be treated usually when the solution is saturated with H.sub.2 SiF.sub.6 to be produced from etching reaction. The exothermic reaction occurs in such mixed acid during treatment and the solution temperature increases by 20.degree. C. in reaction time of 1.about.2 minute(s).
The wafer is etched magnitude of approx. 30 .mu.m. Such vigorous reaction causing the etching damage and control of activity in conventional etchant is usually difficult.
The etching reaction with such mixed acid is as follows. EQU Si+4HNO.sub.3 =SiO.sub.2 +4NO.sub.2 (g)+2H.sub.2 O (1) EQU SiO.sub.2 +6HF=H.sub.2 SiF.sub.6 +2H.sub.2 O (2) EQU 3Si+4HNO.sub.3 +18HF=3H.sub.2 SiF.sub.6 +4NO+8H.sub.2 O (3)
For the treatment of silicon oxide, buffered hydrofluoric acid (BHF) is used, the reaction formula is as follows. EQU 4nHF+SiO.sub.2 =SiF.sub.4.Arrow-up bold.+2H.sub.2 O+nH.sup.-.Arrow-up bold.+nF.sup.-.Arrow-up bold. (4) EQU 2HF+SiF.sub.4 =H.sub.2 SiF.sub.6 (5)
Also, for example, the heated HPM(HCl/H.sub.2 O.sub.2, SPM(H.sub.2 SO.sub.4 +H.sub.2 O.sub.2) and Aqua Regia (HCl+HNO.sub.3) are used to remove heavy metal such as Fe, Cu, Au and the metal such as Al which is difficult to be ionized, wherein spontaneous oxidation layer is made. To remove such oxidation layer, DHF(HF+H.sub.2 O) is used. However, DHF causes extract of Cu on the wafer surface and to solve this problem, the mixed solution of DHF+H.sub.2 O.sub.2 was developed.
However, H.sub.2 O.sub.2 easily decompose into H.sub.2 O+O.sub.2, further HF is easily volatized to make it difficult to maintain the homogeneity of the solution.
Furthermore, the produced fluorosilicon (SiF.sub.4) as above formula (4) reacts with H.sub.2 O to produce colloidal silicon oxide (SiO.sub.2) which easily readheres to the wafer surface. When the colloidal silicon oxide resides on the surface, hazy effect occurs.
Furthermore, the etching rate is an important process parameter but the surface smoothness is also importantly required for the high integrated circuit.
Also, as reaction is proceeding, colloidal silicon oxide and Hydrogen Fluorosilicate accumulate to be disposed, which causes the generation of large amount of waste water. Consequently it is one of the subjects to solve the matter of life time of solution and waste disposal.
Among the various layers to be deposited on LCD and semiconductor wafer, for example, in case of SiNx (ex. Si.sub.3 N.sub.4), higher concentration of HF is required for etching because such etching process is more difficult in comparing with SiO.sub.2, wherein it is impossible to use mask for resist. 85% H.sub.3 PO.sub.4 by boiling method and BOE by wet etch method can be used for etching SiNx but it may cause damage on substrate.
Alternatively plasma etch can be used, however, as throughput is low in plasma etch, it is not feasible for mass production.
For etching Al or Al alloy (ex. Al--Nb, Al--Ta), mixed acid as H.sub.3 PO.sub.4 (65.about.72%)+CH.sub.3 COOH(5.about.15%)+HNO.sub.3 (5.about.8%)+DI water (5.about.25%) is usually used. It is also difficult to attain uniform etching due to the matter that the bubble to be generated from reaction between Al and mixed acid adheres to the surface and difficult to separate from the surface.